First of all you need to have fully installed the game (duh), downloaded the
latest patch and installed that too.

I strongly recommend that you keep all your work in a separate folder. With
all of your edited files in a separate folder, you will never need to worry
about changing any of the original game files. Furthermore, using a
separate folder will make your work much easier to distribute, and also
easier for other players to use.

Create the new folder in the same location
as the Fallout Tactics\core folder. so that the path to your folder looks
like thisC:\Program Files\14 Degrees East\Fallout Tactics\My folder.

Now, in order to make use of the new folder, you will need to use the -path
option to run your game, and your tools.The easiest way to do that is by
making new shortcuts. You only need to make the shortcuts once, and then
use them whenever you like. You will need two shortcuts, one for the game
and one for your editing tools.

Right click on your desktop and choose new shortcut.

Browse to your Fallout Tactics folder and click your FT Tools.exe file. When you click on the file, the path will appear your command line box. The path should be "C:\Program Files\14 Degrees East\Fallout Tactics\FT Tools.exe".

Now edit the box and add this to the end -path My folder. It will look like this "C:\Program Files\14 Degrees East\Fallout Tactics\FT Tools.exe" -path My folder. Click next and enter a name for the new shortcut, and it is finished.

Next you will make another shortcut in exactly the same way, only have it point to BOS.exe instead of FTTools.exe. You will use the FTTools shortcut to start your editing tool, and the the BOS shortcut to play the new levels that you will make.

Next, you will need to unpack three files that the editor needs to work
with.

The tiles are in Fallout Tactics\core\tiles_0.bos.

The entities are in Fallout Tactics\core\entities_0.bos.

The missions are in Fallout Tactics\core\mis-main_0.bos.

Copy these three files from Fallout Tactics\core into Fallout Tactics\My folder.

Rename them to tiles_0.zip, entities_0.zip, and mis-main_0.zip.

Click on tiles_0.zip to open it in winzip, select all files and extract them, make sure that the box is checked to Use Folder Names. Extract the other two files in the same way.

Read through the Editor Readme file a couple of times. No, I'm not kidding,
read it, all of it, for real.
Now use the FTTools shortcut that you made to start up the editor and look it over.